Encapsulation of fragrance and flavor materials is well known in the art. Encapsulation provides advantages to the fragrance/flavor product including the protection of the fragrance/flavor in the capsule core by a shell until the fragrance/flavor is intended to be delivered. In particular, capsules are often designed to deliver their contents at a desired time by the capsule shell being compromised at the desired time.
The capsule shell can be compromised by various factors such as temperature so that the contents are delivered when the capsule begins to melt. Alternatively the capsules can be compromised by physical forces, such as crushing, or other methods that compromise the integrity of the capsule. Additionally, the capsule contents may be delivered via diffusion through the capsule wall during a desired time interval.
It is obviously not desired that the core be released from the shell prematurely. Often, the capsule shell is somewhat permeable to the core contents when stored under certain conditions. This is particularly the case when many capsule types, such as those having aminoplast or cross-linked gelatin walls, are stored in aqueous bases, particularly those containing surfactants. In these cases, although the capsule shell is intact, the fragrance/flavor is removed from the core over time in a leaching process. The overall leaching mechanism may be viewed as a diffusion process, with transfer occurring from the capsule core to the aqueous media, followed by transfer to or solubilization into the surfactant micelles or vesicles. With normal surfactant concentrations of between 1 and 30% in consumer products, as compared to fragrance/flavor levels of 0.3 to 1%, it is clear that the partitioning favors absorption by the surfactant over time.
Bases that are primarily non-aqueous in nature, e.g., those that are based on alcohols, or volatile silicones can also leach fragrance/flavor from capsules over time. In these product types, the base solvent itself solubilizes the fragrance/flavor.
U.S. Pat. No. 6,106,875 discloses a method of encapsulating an amphiphilic volatile flavor or fragrance compound into a microcapsule have a hydrogel shell and an oil core. The flavor or fragrance compound in a liquid is transported into and solubilized into the core using water in the capsule wall to transport the material. The patent discloses that this technique provides a wall thickness and a flavor or fragrance concentration not previously obtainable.
Despite the above teaching and previous encapsulation technologies, there is an ongoing need to develop fragrance/flavor systems which are designed to retain the fragrance/flavor with minimal losses until it is needed and then be able to deliver the fragrance/flavor at the appropriate time.